Present day methods of fabricating optical elements involve generally the steps of casting a blank and polishing its surface or surfaces to the required shape, e.g., concave, convex or aspheric, etc. In the fabrication of mirrors, e.g., of the type used in telescopes, the further step of coating the figured or refigured surface with appropriate reflective material is required. While the foregoing technique has proven quite satisfactory, it includes certain inherent disadvantages. For example, in polishing it is often difficult to figure or refigure the entire surface including edges of an element. Also, polishing a surface may cause "quilting" effects due to polishing pressure. Further, it should be noted that polishing even under computer control may inadvertently remove too much material, thus, in effect, destroying the usefulness of the blank.
The present invention overcomes the above-mentioned disadvantages and provides a method and apparatus for figuring or refiguring an optical surface which is much faster than the polishing method and is applicable to any specular substrate form or material.